AIM: In demyelinating disease spectrum, tumor-like (tumefactive) demyelinating lesions (TDL) are rarely seen. Atypical imaging and clinical features of these lesions may cause misdiagnosis of tumor or abscess.

MATERIAL and METHODS: 25 patients with TDL in our center were followed and clinical, magnetic resonance imaging (MRI), magnetic resonance spectroscopy, cerebrospinal fluid (CSF) findings and disease course were retrospectively evaluated.

RESULTS: Mean age at symptom onset was 29 years. Motor and sensory deficits were most common symptoms and 18 of them were polysymptomatic. Mostly frontal and parietal regions were affected. 10/25 patients were initially misdiagnosed clinically as brain abscess, primary central nervous system tumor metastasis. T2-hypointense rim, incomplete ring enhancement of the lesions on post-gadolinium T1- weighted imaging on brain MRI enabled accurate diagnosis of TDLs. 13 of 21 patients with first-TDL presentation sustained a monophasic course, remaining 8 patients converted to multiple sclerosis (MS) at a mean 38.4 months follow-up. Clinical isolated syndrome (CIS) patients were older than patients who developed MS and Expanded Disability Status Scale was lower (0.96 vs 3.7).

CONCLUSION: Although MRI, CSF and pathologic examination help in differential diagnosis of the mass lesions, close follow-up is still crucial for the definite diagnosis. A higher MS conversion rate was found in patients with a younger TDL onset age.